I have implemented smooth blending between surface textures. Now they blend with each other like in other game engines. Compare the next two screens - before and after the modification. The color change is due to blending of the grass level with the tree level.

Transitions in some places are not smooth, and I don't know why. But I think that it's better to have sharp edges somewhere on the planet. I've left some sharp transitions, shown between rock/grass, because the smooth ones look unrealistic. Some more screenshots: